Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 119, Issue 2, Pages 1224-1233Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp509411v
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Funding
- project Fondazione Cariplo [2010-0612]
- italian MIUR (FIRB) [RBAP114AMK RINAME, RBPR05JH2P Rete ItalNanoNet, RBFR10OAI0 Nanoplasmag]
- INSTM-Regione Lombardia (Mag-Nano)
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We report a broadband H-1 NMR study of the spin dynamics of coated maghemite and goldmaghemite hybrid nanostructures with two different geometries, namely dimers and coreshells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T-B similar to 80 K (maghemite), similar to 105 K (dimer), similar to 150 K (coreshell)), and the magnetization reversal time follows the VogelFulcher law. We observed three different anomalies in H-1 NMR T(1)1 versus T that decrease in amplitude when increasing the applied magnetic field. We suggest that the anomalies are related to three distinct system dynamics: molecular rotations of the organic groups (240 < T < 270 K), superparamagnetic spin blockage (100 < T < 150 K), and surfacecore spin dynamics (T < 25 K). By fitting the T(1)1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.
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